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121.
Lepidomeda albivallis (White River spinedace), a fish species endemic to the White River, Nevada, appeared headed toward extinction. In 1991 only 1 population remained, and it comprised fewer than 50 individuals in a 70-m stream reach. We monitored population recruitment and distribution and studied life history and habitat use from 1993 through 1998. We determined that L. albivallis was not reproducing and was continuing to decline, and as an emergency measure we relocated the population (14 in spring 1995 and 6 in spring 1996) downstream 200 m to a secure habitat that we judged more favorable for reproduction. The relocated population reproduced, and by September 1998 it had increased to 396 individuals that inhabited more than 1 km of stream including both pond and stream habitats. In streams they oriented near the bottom but frequently moved up in the water column to strike at drift items. Gut analysis of museum specimens indicated L. albivallis is omnivorous but feeds primarily upon aquatic invertebrates. Conservation of L. albivallis will require reestablishing additional populations within its former range.  相似文献   
122.
Cover and species richness of vascular and cryptogamic components of the plant community were inventoried in experimental grazing paddocks at the USDA/FS Desert Range Experimental Station, Millard County, Utah. The grazing treatments considered have been applied continuously for over 50 years. The effects of heavy (ca 17 sheep days/acre) grazing treatment applied in two different seasons (early winter versus a split between early and late winter) differed significantly between seasons. Cryptogamic cover and cryptogamic species richness both showed larger decreases under early-late as opposed to early winter only grazing. Vascular plant cover (relative to controls) was also reduced by early-late winter grazing, but not to a significant degree. Late season grazing, likewise, had no significant effect on number of vascular species per transect.  相似文献   
123.
124.
Leu-8/TQ1 is the human equivalent of the Mel-14 lymph node homing receptor   总被引:30,自引:0,他引:30  
D Camerini  S P James  I Stamenkovic  B Seed 《Nature》1989,342(6245):78-82
The human pan-leukocyte antigen Leu-8 has attracted wide interest because its presence or absence identifies suppressor-inducer and helper-inducer CD4+ T-lymphocyte subsets respectively. We report here that Leu-8 is the human homologue of the mouse Mel-14 homing receptor, a molecule that promotes the initial adhesion of blood-borne lymphocytes to the specialized post-capillary endothelium of peripheral lymph nodes. We also show that Leu-8 can adopt both conventional and phospholipid anchored forms, a finding that may have relevance in the context of antigen shedding following activation or homing. The assignment of lymphocytes to different functional classes based on lymph node homing potential may represent a more general association between lymphocyte function and tissue distribution.  相似文献   
125.
J W Slot  R Moxley  H J Geuze  D E James 《Nature》1990,346(6282):369-371
A major effect of insulin is to increase glucose transport in muscle and fat. A family of genes encoding distinct mammalian glucose transporters has recently been elucidated. One of these, the insulin-regulatable glucose transporter (IRGT), is primarily expressed in muscle and fat, tissues that exhibit insulin-dependent glucose transport. Insulin promotes glucose transport in these tissues by stimulating movement of the glucose transporter from an intracellular location to the plasma membrane. Recent studies, however, suggest that an additional effect of insulin in these tissues may be the facilitation of glucose transport, presumably across capillary endothelium. This hypothesis is based on the localization of the IRGT in endothelial cells specific to muscle and adipose tissue. We report here, however, on morphological and biochemical studies using several different IRGT-specific antibodies in which we could not reproduce these results.  相似文献   
126.
本书是初等数论的引论,供大学数学系高年级学生用作一学期的教材,其前身是作者在美国Providence学院和西点军校的讲稿。第二版对原版作了全面增订,增加了历史材料,强调了初等数论的应用,并添加了375道习题。  相似文献   
127.
The strategic roles of modern business leaders are both demanding and diversified. Leaders all around the world are tied up with daily schedules, public as well as private. But it is almost self-evident that they should come out from all these trivial items and only focus on three key things: Strategic thinking and decision-making, branding position of their orga- nization and quality and long-term sustainability of core service of business. Business schools and programs all around the world are tapping into this mar- keting opportunity and try to free business leaders from daily tie-ups and really pay attention to the above-mentioned agenda.  相似文献   
128.
From 1972 to 1982 three exceptionally large sauropod scapulocoracoids and other equally large sauropod bones were collected from the base of the Brushy Basin Member of the Upper Jurassic, Morrison Formation, in western Colorado. Two of the scapulae are conspecific, but the third represents a second genus and possibly a new family. The two conspecific specimens are described here as: Supersaurus vivianae ; the second genus is described as Ultrasaurus mcintoshi , and a large, robust anterior dorsal vertebra of unique form is described as Dystylosaurus edwini . Various miscellaneous elements are referred to the three genera.      相似文献   
129.
A radiation hybrid map of the rat genome containing 5,255 markers.   总被引:17,自引:0,他引:17  
A whole-genome radiation hybrid (RH) panel was used to construct a high-resolution map of the rat genome based on microsatellite and gene markers. These include 3,019 new microsatellite markers described here for the first time and 1,714 microsatellite markers with known genetic locations, allowing comparison and integration of maps from different sources. A robust RH framework map containing 1,030 positions ordered with odds of at least 1,000:1 has been defined as a tool for mapping these markers, and for future RH mapping in the rat. More than 500 genes which have been mapped in mouse and/or human were localized with respect to the rat RH framework, allowing the construction of detailed rat-mouse and rat-human comparative maps and illustrating the power of the RH approach for comparative mapping.  相似文献   
130.
Henry Rogers Durkee collected 74 egg sets of 27 avian species in 1870 at Gilmer, Uinta County, in southwestern Wyoming. Despite the paucity of documented breeding evidence from this region during the late 19th and early 20th centuries, his material at the Smithsonian Institution was generally overlooked and has never been critically examined. Durkee's egg sets included 5 species (Sandhill Crane, Grus candensis ; Northern Rough-winged Swallow, Stelgidoteryx serripennis ; Grasshopper Sparrow, Ammodramus savannarum ; Fox Sparrow, Passerella iliaca ; Cassin's Finch, Carpodacus cassinii ) whose breeding distribution was then poorly known, 25 to more than 70 years before nests and eggs were otherwise documented in Wyoming. Durkee also collected complete egg sets of Lark Bunting ( Calamospiza melanocorys ) over 70 years before breeding was confirmed at other peripheral locations in Wyoming. In addition, Durkee's incomplete egg sets of Grasshopper Sparrow were the 1st western subspecies ( A. s. perpallidus ); his complete egg set and nest of the Fox Sparrow collected at Gilmer constituted the 2nd locality for the species or species group ( P. i. schistacea ). Although the number of egg sets Durkee collected is modest, he made a meaningful contribution to the early history of avifaunal exploration in Wyoming.  相似文献   
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